This invention relates to control devices for vehicles, and more particularly to control devices including: the anti-skid braking system for controlling the braking force on the basis of the velocity information of the road wheels of the vehicle, and the power steering control system for providing an assisting steering torque on the basis of the information upon the steering torque and the vehicle velocity.
Generally, the anti-skid braking system and the power steering control system for vehicles are implemented separately. FIG. 5 is a block diagram showing the structure of a conventional power steering control system of a vehicle. A torque sensor 1 detects the steering torque of the steering wheel 100 of the vehicle. The first and the second vehicle velocity sensors 2a and 2b detect the velocity of vehicle relative to the ground. The outputs from the torque sensor 1, the first and the second vehicle velocity sensors 1a and 1b, etc., are input through the interface 3 to a main microcomputer 4 and a sub-microcomputer 5 of the control device. The main microcomputer 4 calculates the requisite assisting steering torque, etc., on the basis of the steering torque information and the vehicle velocity relative to the ground, input through the interface 3. The sub-microcomputer 5 performs similar calculations as the main microcomputer 4 based on similar inputs.
A fail-safe relay 6 is coupled to the main microcomputer 4 and the sub-microcomputer 5. The fail-safe relay 6 is activated upon receiving the outputs from the main microcomputer 4 and the sub-microcomputer 5, to supply the power of the battery 7 to a motor drive circuit 8 and a clutch drive circuit 10, etc. The motor drive circuit 8 coupled to the main microcomputer 4 and the sub-microcomputer 5 outputs the drive signal to a DC motor 9 providing an assisting steering torque, on the basis of the outputs from the microcomputers 4 and 5. The clutch drive circuit 10 outputs the drive signal to the clutch 11 on the basis of the output received from the main microcomputer 4.
The power steering control system of FIG. 5 thus includes two microcomputers 4 and 5, and the control signal is output when the outputs of the two microcomputers coincide with respect to the driving condition of motor drive circuit 8. The control device is fail-safe in that the control signal is output only when the results of the calculations of the two microcomputers are the same.
FIG. 6 is a block diagram showing the structure of a conventional anti-skid braking system of a vehicle. The road wheel velocity sensors 21a through 21d detect the velocities of the road wheels of the vehicle. A brake switch 22 is activated upon operation of the brake by the driver of the vehicle. The outputs from the road wheel velocity sensors 21a through 21d and the brake switch 22, etc., are supplied to a master microcomputer 24 and a slave microcomputer 25 through an interface 23. The master microcomputer 24 calculates the brake operation signal for the road wheels (namely, the control signal for increasing and decreasing the braking pressure) on the basis of the information upon the velocity of the road wheels and the braking operation. The slave microcomputer 25 performs similar calculations as the master microcomputer 24 based on similar inputs.
A watch dog circuit 26 monitors the operations of the master microcomputer 24 and the slave microcomputer 25. The drive circuit 27 takes the logical product, for example, of the outputs of the microcomputers 24 and 25 and the watch dog circuit 26, to generate the drive signal for a fail-safe main relay 28. Upon receiving the drive signal from the drive circuit 27, the fail-safe main relay 28 is energized to supply the power from the battery 29 to a valve drive circuit 30 and a hydraulic unit 31, etc.
On the basis of the outputs received from the master microcomputer 24, the valve drive circuit 30 supplies the drive signals to the hydraulic unit 31. Upon receiving a drive signal, the hydraulic unit 31 activates a built-in electromagnetic valve thereof, thereby adjusting the pressure of the master cylinder supplied to the wheel cylinders.
The anti-skid braking system of FIG. 6 thus includes two microcomputers 24 and 25, and the watch dog circuit monitors the operations of the two microcomputers to judge whether or not the microcomputers are operating normally. Unless the two microcomputer operate normally, the fail-safe function is put into operation to ensure the safety of the vehicle. The recent anti-skid braking system thus generally includes two microcomputer with an increased redundancy, to provide for increased safety.
The conventional control device for a vehicle thus includes a power steering control system and an anti-skid braking system that are implemented separately. The power steering control system and the anti-skid braking system each include two microcomputers to ensure safety. The information upon the steering torque and the vehicle velocity is necessary for the power steering control system and the information upon the velocity of the road wheels is necessary for the anti-skid braking system. The control device including a number of microcomputers becomes large-sized and expensive. The wiring of the vehicle harness (i.e., the signal lines) becomes complicated. Further, if the power steering control system and the anti-skid braking system are combined and unified mechanically, the failure of the one system results in the halting of operation of the other and the fail-safe functions thereof may be nullified.